Application of Urban Inundation Model in Flood Mitigation of Detention Pond

The causes of inundation in urban areas were numerous and complex. Even though there were flood mitigation facilities, once the rainfall intensity and the downstream tidal level were exceedingly high, the flood in drainage could not be drained in time or even overflow. Detention pond was an important flood mitigation facility in recent years. However, the detention efficiency might be affected by the timing of the operation. The harmful runoff that cannot be drained caused flooding in the urban areas. In order to avoid the problem of flooding in the local area caused by the superposition of runoff, it was necessary to analyze the surface runoff of the urban areas caused by the storm events on the basis of the current flood mitigation facilities.

The establishment of the PHD model was carried out to test the calculus of Typhoon Nesat in 2017, extremely heavy rainfall events 0823 in 2018 and 0813 in 2019 as a verification case. The water level between the simulated and measured results of the typhoon and rainfall events was compared. These results shows a good agreement in the peak value of water level, and the PHD model can reasonably calculate the runoff.

Analyze the optimal conditions of the detention facilities. Based on two consecutive 10-year heavy rain events (with an interval of 12 hours), and start pumping at different delays, calculate the water depth to analyze the flood reduction effect of the detention facilities. Analysis of the flood reduction effect based on the average reduction of water depth, the results show that when the pumping is started about 4 hours after the flood peak, the effect of lowering the water level of the detention pond can be better.